You can Special Summon this card (from your hand) by discarding 1 other WATER monster. When this card is Summoned: You can send 1 Level 2 or lower Aqua-Type WATER monster from your Deck or face-up from your field to the Graveyard. Once per turn: You can return 1 monster you control to the hand; you can Normal Summon 1 "Frog" monster during your Main Phase this turn, except "Swap Frog", in addition to your Normal Summon/Set. (

You can only gain this effect once per turn.)

This now brings it in line with the OCG Rulings:

Even if you control 2 or more copies of "Swap Frog", you can only activate the effect "Once per turn, you can return 1 monster you control to your hand to Normal Summon 1 "Frog" monster, except "Swap Frog" or "Frog the Jam", in addition to your Normal Summon or Set this turn." of 1 of them. During the turn this effect is applied, since the number of Normal Summons cannot be increased by the effect of "Swap Frog", the effect of a second copy of "Swap Frog" cannot be activated that turn.